Capacitive detection, energy transfer, and/or data transfer system

ABSTRACT

A system is disclosed, comprising a base and at least a first moveable entity, the first moveable entity being moveable with respect to the base and positionable in at least a first position with respect to the base. The base comprises a first base electrode and a second base electrode, and the movable entity comprises a first moveable entity electrode and a second moveable entity electrode. The electrodes are arranged such that when the moveable entity is in the first position the first base electrode and the first moveable entity electrode align to form a first capacitor and the second base electrode and second moveable entity electrode align to form a second capacitor. The first moveable entity further comprises a first resistor connecting the first moveable entity electrode to the second moveable entity electrode, and the base further comprises: signal supply means arranged to supply a time-varying electrical signal to the first base electrode; and signal detection means arranged to detect an electrical signal from the second base electrode.

This application is a continuation of U.S. Ser. No. 15/313,455, filedNov. 22, 2016 (allowed), which is a 371 of PCT/GB2015/051528, filed May26, 2015, which claims priority to G.B. Serial No. 1409182.1, filed May23, 2014 and G.B. Serial No. 1414916.5, filed Aug. 21, 2014, each ofwhich are hereby incorporated by reference.

Certain aspects of the present invention generally relate to systems inwhich it is necessary or desirable to be able to detect when a moveableentity is arranged in a particular position with respect to anotherentity, such as a base. In particular, although not exclusively, certainaspects of the present invention relate to systems in which it isdesirable or necessary to identify the moveable entity when it islocated in the predetermined position. Certain aspects additionally, oralternatively, relate to systems in which energy and/or data istransferred between two entities, for example bi-directionally.

BACKGROUND

There are numerous applications in which it is desirable or necessary tobe able to detect when a moveable entity is placed in a predeterminedposition with respect to another entity, such as a base. There arenumerous applications where additionally it is necessary or desirable tobe able to identify the moveable entity when it is located in thepredetermined position, for example where the moveable entity is one ofa number of moveable entities that can each be arranged in thepredetermined position.

It is known, for example, to use RF ID tags in such applications. Eachtag typically comprises a circuit including an inductor and the base isarranged to generate an electromagnetic field in a defined region. Whenthe RF ID tag is brought into that defined region there is inductivecoupling between the base and the RF ID tag. This inductive coupling maybe arranged to supply energy to the RF ID tag, which may then transmit asignal to the base, that signal enabling the base to identify theparticular RF ID tag.

Whilst such tagging systems find a wide variety of applications, theyare relatively complex, and the necessity for each tag to include arespective inductor poses challenges both to attempts to reduce thecomplexity of the system and to reducing the cost of the tags.

BRIEF SUMMARY OF THE DISCLOSURE

Embodiments of the present invention aim to solve, at least partly, atleast one of the problems associated with the prior art.

Certain embodiments of the invention aim to provide a simple and lowcost system for detecting and identifying a moveable entity placed in apredetermined position with respect to another entity, such as a base.

Certain embodiments aim to provide a system in which the componentsincorporated in each of a plurality of moveable entities, to enable abase to be able to identify and distinguish between the differentmoveable entities, consist of simple and low cost components, which maybe produced by techniques such as printing, for example.

Certain embodiments aim to provide a system in which the electricalelements in the moveable entity enabling it to be detected andidentified by a base, or other entity, do not include any inductor.

A first aspect of the invention provides a system comprising a base (orother first entity) and at least a first moveable entity, the firstmoveable entity being moveable with respect to the base and positionablein at least a first position with respect to the base,

-   -   the base comprising a first base electrode and a second base        electrode, and the moveable entity comprising a first moveable        entity electrode and a second moveable entity electrode,    -   said electrodes being arranged such that when the moveable        entity is in said first position the first base electrode and        the first moveable entity electrode align to form a first        capacitor and the second base electrode and second moveable        entity electrode align to form a second capacitor,    -   the first moveable entity further comprising a first resistor        connecting the first moveable entity electrode to the second        moveable entity electrode,    -   and the base further comprising:    -   signal supply means arranged to supply a time-varying electrical        signal to the first base electrode; and    -   signal detection means arranged to detect an electrical signal        from the second base electrode.

Advantageously, the coupling between the base and the moveable entity ispurely capacitive; the coupling is non-inductive. Detection of themoveable entity being in the first position is achieved withoutrequiring any inductor in the moveable entity.

It will be appreciated that the base referred to above may also bedescribed as a first entity. In certain embodiments, the base itself maybe a moveable, portable, or otherwise mobile entity. In alternativeembodiments, the base may be substantially fixed in a particularlocation.

In certain embodiments, the moveable entity electrodes and firstresistor may be incorporated in a body or housing of the moveableentity, for example, in alternative embodiments, the moveable entityelectrodes and first resistor may be incorporated in a tag attached tothe remainder of the moveable entity.

Advantageously, as the moveable entity only requires electricalcomponents consisting of the first and second moveable entity electrodesand first resistor to be detected, and optionally identified, by thebase, it can be produced at lower cost, and more simply than prior artmoveable entities incorporating RF ID prior art moveable entitiesincorporating RF ID tags.

It will be appreciated that, when the moveable entity is arranged in thefirst position, there is capacitive coupling between the base and themoveable entity, resulting in an electrical signal being developed atthe second base electrode which is then detected by the detection means.

In certain embodiments, the signal detection means can detect, from theelectrical signal from the second base electrode, whether the firstmoveable entity is in said first position.

In certain embodiments said time-varying electrical signal is a squarewave voltage signal.

Certain alternative embodiments may employ a time-varying electricalsignal having a different form, such as a sinusoidal signal. However,use of a square wave signal comprising a plurality of rapid transitionsprovides the advantage that, if the values of R, C and T are arrangedappropriately, the signal developed at the second base electrode maycomprise a plurality of peaks, having at least one feature indicative ofthe resistance of the first resistor, so enabling the detection means todetermine (i.e. identify) the resistance of the first resistor, or atleast be able to distinguish it from at least one other resistance valuethat may be incorporated in another moveable entity that is alsoarrangeable in the first position.

It will be appreciated that the term “square wave” is being used in abroad sense to encompass any cyclical signal comprising relatively rapidtransitions between a low state and a high state, and does not requirethe durations of the high state and low state cautions of the cyclenecessarily to be of equal length.

In certain embodiments, the base comprises a ground rail and the signaldetection means comprises a base resistor arranged to connect the secondbase electrode to the ground rail.

In certain embodiments, the square wave voltage signal has a time periodT, the first resistor has a resistance R1, the base resistor has aresistance Rb, the first capacitor has a capacitance C1, and the secondcapacitor has a capacitance C2, and RC<T, where R=R1+Rb, and(1/C)=(1/C1)+(1/C2).

Arranging RC to be less than T results in the signal of the second basecapacitor having a form comprising a plurality of peaks. Advantageously,in certain embodiments RC is arranged to be substantially smaller thanT, enhancing the peaked form of the output signal. For example, RC maybe less than 0.25 T, 0.2 T, 0.1 T, or even smaller.

In certain embodiments RC<0.1 T

In certain embodiments R, C, and T are arranged such that the electricalsignal from the second base electrode is a time-varying voltagecomprising a plurality of peaks.

In certain embodiments said peaks have a height indicative of R1.

In certain embodiments, the signal detection means further comprises:

-   -   a diode having a first terminal and a second terminal, the first        terminal being connected to the second base electrode; and    -   a further resistor and a further capacitor connected in parallel        with one another between the diode second terminal and the        ground rail.

In certain embodiments, a voltage at the diode second terminal issubstantially a DC voltage having a magnitude indicative of a height ofsaid peaks.

In certain embodiments, the signal detection means comprises comparatormeans arranged to compare said DC voltage, or a voltage derived fromsaid DC voltage, with at least one reference voltage.

Such an arrangement provides the advantage that a relatively simple, andlow cost detection circuit may be arranged to distinguish the moveableentity from another moveable entity, having a different first resistorwith a different resistance, which may also be placed in the firstposition.

In certain embodiments, the signal detection means is adapted todetermine the resistance of the first resistor from the electricalsignal from the second base electrode.

In certain embodiments, each of the first and second base electrodes andeach of the first and second moveable entity electrodes comprises arespective flat plate.

In certain embodiments, the first base electrode comprises a firstrectangular plate, and the second base electrode comprises a secondrectangular plate arranged parallel to the first rectangular plate.

In certain embodiments, the first moveable entity electrode comprises athird rectangular plate, and the second moveable entity electrodecomprises a fourth rectangular plate arranged parallel to the thirdrectangular plate.

In certain embodiments, the first base electrode comprises a firstsectorial plate and the second base electrode comprises a secondsectorial plate.

In certain embodiments, the first and second sectorial plates arearranged as adjacent sectors within a circular boundary.

In certain embodiments, the first and second sectorial plates arearranged as diagonally opposite sectors within a circular boundary.

In certain embodiments, the first moveable entity electrode comprises athird sectorial plate and the second moveable entity electrode comprisesa fourth sectorial plate.

In certain embodiments, the third and fourth sectorial plates arearranged either as adjacent sectors or diagonally opposite sectorswithin a circular boundary.

It will be appreciated that the use of sectorial plates in the baseand/or moveable entity in certain embodiments can enable the system todistinguish between a plurality of different rotational arrangements ofthe moveable entity with respect to the base. In other words, the basemay be able not just to detect the identity of the moveable entity, butalso which, of a plurality of rotational positions of the moveableentity with respect to the base, the moveable entity is arranged in.

In certain embodiments, the first base electrode comprises a firstcircular plate, the second base electrode comprises a first annularplate surrounding the first circular plate, the first moveable entityelectrode comprises a second circular plate, and the second moveableentity electrode comprises a second annular plate surrounding the secondcircular plate.

Such an arrangement provides the advantage that the detection system maybe insensitive to the particular rotational arrangement of the moveableentity with respect to the base unit at the first position. In otherwords, if the circular plates are aligned with respect to each other,and so are the respective annular plates, then the same capacitivecoupling is achieved between the base and the moveable entity,irrespective of the particular rotational orientation of the moveableentity about an axis particular to the planes of the circular plates andthrough their centres.

It will be appreciated, however, that in alternative embodimentsdifferent arrangements of plates may be used such that the capacitivecoupling between the base and moveable entity is dependent upon themoveable entity being in a correct rotational position with respect tothe base.

In certain embodiments, the first base and moveable entity electrodeshave substantially the same size and shape as one another.

In certain embodiments, the second base and moveable entity electrodeshave substantially the same size and shape as one another.

In certain embodiments, the first moveable entity further comprises athird moveable entity electrode and a second resistor connecting thefirst moveable entity electrode to the third moveable entity electrode,the first and second resistors have different resistances, and themoveable entity electrodes are arranged such that the moveable entity ispositionable in a second position with respect to the base in which thefirst base electrode and the first moveable entity electrode align toform a first capacitor and the second base electrode and third moveableentity electrode align to form a second capacitor.

In certain embodiments, the signal detection means is adapted todetermine which of the first and second positions the moveable entity ispositioned in with respect to the base from the electrical signal fromthe second base electrode.

In certain embodiments, the first base electrode comprises a firstcircular plate, the second base electrode comprises a second plateseparated in a radial direction from a centre of the first circularplate.

In certain embodiments, the first moveable entity electrode comprises asecond circular plate, the second moveable entity electrode comprises aplate separated in a first radial direction from a centre of the secondcircular plate, and the third moveable entity electrode comprises aplate separated in a second radial direction from the centre of thesecond circular plate.

In certain embodiments, the system comprises a plurality of saidmoveable entities, each moveable entity being moveable with respect tothe base and positionable in at least said first position with respectto the base, each moveable entity comprising a respective first moveableentity electrode and a respective second moveable entity electrode, saidelectrodes being arranged such that when any one of said moveableentities is in said first position the first base electrode and therespective first moveable entity electrode align to form a respectivefirst capacitor and the second base electrode and the respective secondmoveable entity electrode align to form a respective second capacitor,each moveable entity further comprising a respective first resistorconnecting the respective first moveable entity electrode to therespective second moveable entity electrode.

In certain embodiments, the resistances of the respective firstresistors are different from one another.

In certain embodiments, the signal detection means is adapted todetermine (identify), when one of the plurality moveable entities isarranged in said first position, which one of said entities is arrangedin said first position from the electrical signal from the second baseelectrode.

It will be appreciated that certain systems embodying the invention cantherefore be described as capacitive coupling identification systems.Without requiring the moveable entities to be provided with inductors,the systems embodying the invention are able to provide a simpler, andlower cost tagging system, where the different moveable entities can beidentified from their characteristic resistances, via capacitivecoupling with the base.

In certain embodiments, the first and second base electrodes form afirst pair of electrodes, and the base comprises a plurality of saidpairs of electrodes, each pair comprising a respective first baseelectrode and a respective second base electrode, the first moveableentity being moveable with respect to the base and positionable in atleast a plurality of first positions with respect to the base, eachfirst position corresponding to alignment between the moveable entityelectrodes and the first and second electrodes of a respective pair offirst and second base electrodes,

the pairs of electrodes and the moveable entity electrodes beingarranged such that when the moveable entity is in any one of said firstpositions the respective first base electrode of the respective pair andthe first moveable entity electrode align to form a respective firstcapacitor and the respective second base electrode of the respectivepair and second moveable entity electrode align to form a respectivesecond capacitor,

and wherein the signal supply means is arranged to supply saidtime-varying electrical signal to each first base electrode, and thesignal detection means is arranged to detect an electrical signal fromeach second base electrode.

Such systems may also comprise a plurality of moveable entities, eachwith a respective first resistor having a characteristic value asdescribed above. Thus, the system can provide the advantage that thebase is able to detect not just whether a moveable entity has beenplaced at one of the first positions, but also the identity of themoveable entity at that position. There are a wide variety ofapplications for such systems.

In certain embodiments, the signal supply means comprises multiplexingmeans operable to selectively supply said time-varying electrical signalto the first base electrodes.

The signal supply means may be arranged to operate the multiplexingmeans so that the time-varying electrical signal is supplied to just oneof the first base electrodes at a particular time. Alternatively, thesignal supply means may comprise the multiplexing means so as to supplythe time-varying electrical signal to a selected sub-set of theplurality of first base electrodes at the same time. In alternativeembodiments, however, the signal supply means may comprise nomultiplexing means, and the signal supply means may be arranged tosupply the time-varying electrical signal to all of the first baseelectrodes at the same time.

In certain embodiments, the signal detection means comprisesmultiplexing means operable to permit selected detection of anelectrical signal from any one of said second base electrodes.

The signal detection means may be arranged to operate the multiplexingmeans such that the electrical signal from just one of the second baseelectrodes is processed or monitored at a particular time. For example,the signal detection means may be arranged to operate the multiplexingmeans so as to provide sequential monitoring of the electrical signalfrom the plurality of second base electrodes. For example, the pluralityof second base electrodes may be sequentially poled so as to determinewhether a moveable entity is located in the relevant position, and alsoto determine the identity of any such moveable entity at that position.

Another aspect of the invention provides a system comprising a base (orother first entity) and at least a first moveable entity, the firstmoveable entity being moveable with respect to the base and positionablein at least a first position with respect to the base,

-   -   the base comprising at least a first base electrode, and the        moveable entity comprising at least a first moveable entity        electrode, and    -   said electrodes being arranged such that when the moveable        entity is in said first position the first base electrode and        the first moveable entity electrode are coupled (e.g.        capacitively) to form a first capacitor,    -   the base further comprising signal supply means, arranged to        supply a first time-varying electrical signal to the first base        electrode, and    -   the first moveable entity further comprising circuitry connected        to the first moveable entity electrode.

It will be appreciated that features of the previously-described aspectsand embodiments may be incorporated in embodiments of this furtheraspect, with corresponding advantages.

In certain embodiments said base is arranged to power said circuitry viasaid time-varying electrical signal and the coupling between the firstbase electrode and the first moveable entity electrode when the firstmoveable entity is in the first position.

In certain embodiments said time-varying electrical signal carries dataand said circuitry is arranged to detect said data when the firstmoveable entity is in said first position.

In certain embodiments the base further comprises signal detection meansarranged to detect an electrical signal from the first base electrode.

In certain embodiments the signal detection means is adapted todetermine whether the first moveable entity is in said first positionfrom the electrical signal from the first base electrode.

In certain embodiments the signal detection means is adapted todetermine an identity of the first moveable entity when the firstmoveable entity is in said first position from the electrical signalfrom the first base electrode.

In certain embodiments said circuitry is arranged to provide a secondtime-varying electrical signal to the first moveable entity electrode,the second time-varying electrical signal carrying second data, and thesignal detection means is adapted to detect said second data when thefirst moveable entity is in said first position (i.e. via the capacitivecoupling between the electrodes).

In certain embodiments said circuitry comprises:

-   -   a first node, connected to the first moveable entity electrode,        a second node, and a third node;    -   a first diode connected between the first node and the second        node to allow current flow from the first node to the second        node and block current flow from the second node to the first        node; and    -   a second diode connected between the third node and the first        node to allow current flow from the third node to the first node        and block current flow from the first node to the third node.

In certain embodiments said circuitry further comprises a secondcapacitor connected between the second node and the third node. Thus, incertain embodiments a voltage is developed across the second capacitor(i.e. between the second and third nodes) in response to the firsttime-varying electrical signal being applied to the first base electrodewhen the first moveable entity is in said first position.

In certain embodiments said circuitry further comprises a resistorconnected between the second node and the third node. Thus, in certainembodiments an electrical current is driven through said resistor (i.e.between the second and third nodes) in response to the firsttime-varying electrical signal being applied to the first base electrodewhen the first moveable entity is in said first position.

In certain embodiments said circuitry further comprises data detectionmeans connected to the second and third nodes and adapted to detect datacarried by the first time-varying electrical signal from a signaldeveloped between the second and third nodes when the first moveableentity is in said first position.

In certain embodiments said circuitry further comprises datatransmission means connected to the second and third nodes and adaptedto supply a second time-varying electrical signal carrying second datato the first moveable entity electrode.

In certain embodiments said circuitry further comprises power supplycircuitry connected to the second and third nodes, adapted to receivepower via the second and third nodes when the first moveable entity isin said first position, and adapted to power at least one of the datadetection means and the data transmission means using said receivedpower.

In certain embodiments the first moveable entity comprises a firstportion, and a second portion attached to the first portion, wherein thesecond portion comprises the first moveable entity electrode and saidcircuitry.

In certain embodiments said second portion is a label attached to asurface of the first portion.

In certain embodiments said first portion comprises a container.

In certain embodiments said container is one of: a plastic container;and a metal container.

In certain embodiments said container is at least partly filled withliquid or solid contents.

In certain embodiments the coupling between the first base electrode andthe first moveable entity electrode to form the first capacitor is atleast partly via the first portion.

In certain embodiments the first portion comprises a container having awall, and optionally at least partly filled with contents, and saidcoupling is at least partly via said wall, and optionally at leastpartly via said contents.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to theaccompanying drawings, of which:

FIG. 1 is a schematic representation of a first system embodying theinvention;

FIG. 2 is a schematic representation of another system embodying theinvention;

FIG. 3 is a schematic representation of another system embodying theinvention;

FIG. 4 illustrates some of the components of another system embodyingthe invention;

FIG. 5 illustrates the application of a square wave input voltage topart of the system embodying the invention;

FIGS. 6, 7 and 8 show different output wave forms from the arrangementof circuit components shown in FIG. 5 for different values of RCrelative to the period T of the square wave input signal;

FIGS. 9 and 10 respectively show the arrangement of moveable entityelectrodes and base electrodes in a system embodying the invention;

FIGS. 11 and 12 respectively show the arrangement of moveable entityelectrodes and base electrodes in another system embodying theinvention;

FIGS. 13 and 14 respectively show the arrangement of moveable entityelectrodes and base electrodes in another embodiment of the invention;

FIGS. 15 and 16 respectively show the arrangement of moveable entityelectrodes and base electrodes in another embodiment of the invention;

FIG. 17 is a schematic representation of another system embodying theinvention;

FIGS. 18-21 show the arrangement of moveable entity electrodes and baseelectrodes in a number of different embodiments to the invention;

FIG. 22 is a schematic representation of another system embodying theinvention;

FIG. 22A is a schematic representation of an alternative electrodearrangement employed in other embodiments of the invention; and

FIGS. 23-30 show further embodiments of the invention.

DETAILED DESCRIPTION

Referring now to FIG. 1, this is a highly schematic representation of acapacitive detection and identification system embodying the invention.The system comprises a first entity 1, which in this example is a base.The system also includes a moveable entity 2 which is moveable withrespect to the base and positionable in a first position P1 with respectto the base. In this first example, in the first position P1 a flatlower surface 200 of the moveable entity 2 is generally resting on aflat upper surface 100 of the base, but in alternative embodiments thedetails of the engagement between the moveable entity and the baseentity may be different. For example, the base entity may have a curvedor contoured surface against which the moveable entity rests when in thefirst position. Also, in certain embodiments the surface of the baseagainst which the moveable entity is located when in the first positionis not necessarily horizontal. It could, for example, be a verticalsurface, and the moveable entity could comprise means for holding it inthat first position. These means could, for example, include one or moremagnets, or other such means for temporarily holding the moveable entityin the first position in a releasable manner. Also, in alternativeembodiments the moveable entity could simply be placed next to anon-horizontal surface of the base when in the first position, forexample with a side surface of the moveable entity being adjacent to theelectrodes in the base, the moveable entity being supported in somemanner.

Returning to the present embodiment, the base comprises a first pair ofelectrodes, consisting of a first electrode 11 (which will be describedas a first base electrode) and a second electrode 12 (which will bedescribed as a second base electrode). The moveable entity 2 comprises acorresponding pair of electrodes which consist of a first electrode 21(which will be described as a first moveable entity electrode) and asecond electrode 22 (which will be described as a second moveable entityelectrode). The four electrodes in the figure are arranged such thatwhen the entity 2 is in the first position P1 the first base electrode11 and the first moveable entity electrode 21 align to form a firstcapacitor C1 and the second base electrode 12 and second moveable entityelectrode 22 align to form a second capacitor C2. The entity 2 furthercomprises a first resistor 23 connecting electrode 21 to electrode 22.The base further comprises signal supply means 3 arranged to supply atime-varying electrical signal to the first base electrode 11. The basealso comprises signal detection means 4 arranged to detect an electricalsignal from the second base electrode 12.

When the entity 2 is located in position P1 it is capacitively coupledto the base, and the application of the time varying signal to baseelectrode 11 results in the generation of an electrical signal at thesecond base electrode 12, which is detected by the detection means 4.When the entity 2 is moved away from position P1, the capacitivecoupling is broken, and no signal is detected at the second baseelectrode 12. Thus, the system provides a simple and inexpensive meansof detecting when the entity 2 is in the first position P1.

In certain embodiments, the signal detection means 4 is adapted todetermine the resistance of the first resistance 23 from the signal atthe second base electrode 12, as will be appreciated from the followingdescription. The system may thus be able to determine whether the entityis in the first position, and also determine the identity of the entity.

Referring now to FIG. 2, this shows another system embodying theinvention in which the base unit 1 comprises two pairs of baseelectrodes, each pair associated with a respective first position P1A,P1B in which a moveable entity 2 may be located to provide capacitivecoupling between the base and entity. The first pair of base electrodescomprises electrodes 11A and 12A, and the second pair of base electrodescomprises electrodes 11B and 12B. The moveable entity 2 is shown in aposition P1B in which its electrodes 21 and 22 form respective first andsecond capacitors with base electrodes 11B and 12B. In this position,entity 2 is not capacitively coupled to the first pair of baseelectrodes 11A, 12A. The signal supply means is arranged to supply atime varying signal to both the first base electrodes 11A, 11B and thesignal detection means is arranged to detect electrical signals fromeach of the second base electrodes 12A, 12B. The signal detection means4 is adapted to determine, from the signals developed at the second baseelectrodes, when moveable entity is located in one of the positions P1A,and P1B, and the signal detection means can further distinguish from thedetected signals which, of those two positions, the entity 2 is arrangedin. Referring now to FIG. 3, this shows another system embodying theinvention and comprising a base 1 and two moveable entities 2A, 2B,which may also be described as mobile devices. Each mobile devicecomprises a respective pair of electrodes 21A, 22A and 21B, 22B, and arespective resistor 23A, 23B. The resistors 23A and 23B have differentresistances from one another (in other words the mobile devices comprisecharacteristic or identifying resistors connecting their capacitorplates) and this enables the base to determine which of the two mobiledevices is in the first position P1 when either one of the devices islocated in this manner. In this embodiment, the signal supply means isarranged to supply a generally square wave voltage signal S to the firstbase electrode 11 via an input terminal 300. When one of the mobiledevices is located in the first position P1 its electrodes arecapacitively coupled to the base electrodes 11, 12 and this results inthe generation of a voltage on the second base electrode 12. In thisembodiment, the signal detection means further comprises a secondresistor 42, which may also be described as a base resistor havingresistance Rb, connecting the second base electrode 12 to a ground rail41 of the base. As the input voltage signal S is applied to the terminal300, the first and second capacitors C1 and C2 alternately charge andthen discharge, via series resistors 23A and 42. The time constantdetermining this charging and discharging is given by RC, where R=R1+Rb(where R1 is the resistance of the first resistor 23A) and C is thetotal capacitance of the series arrangement of first and secondcapacitors, where (1/C)=(1/C1)+(1/C2). If T is the period of the squarewave signal S, then if RC is substantially less than T, the voltagedeveloped on the second capacitor plate 12 comprises a series of pulses,each having a magnitude dependent upon R1. The rapidity with which eachof these pulses decays to a base line is determined by RC.

In this embodiment, the signal detection means 4 further comprises adiode 43 having a first terminal connected to the second base electrode12 (in the figure this first terminal of the diode is shown connected toa node between the second base electrode 12 and the resistor 42) and thediode has a second terminal connected to a nominal output signalterminal 400. The signal detection means 4 further comprises a furtherresistor 44 and a further capacitor 45 connected in parallel with oneanother between the diode second terminal and the ground rail 41. Theincorporation of the diode 43 and further resistor 44 and capacitor 45results in the output signal at terminal 400 being substantially a DCsignal having a magnitude proportional to the height of the voltagepulses developed on the second base electrode 12. In certain embodimentsthe signal detection means 4 is able to determine from the signal atterminal 400 which of the two moveable devices 2A, 2B is arranged in thefirst position P1, as the magnitude of the signal at terminal 400 isdependent upon the magnitude of the resistance R1 of the moveable entityresistor 23A or 23B.

It will be appreciated that the system shown in FIG. 3 comprises a baseand multiple mobile devices. The base system supplies an input squaresignal with a predefined amplitude and frequency to the first baseelectrode 11. The base system provides an analogue output signal (atterminal 400) allowing the base to identify (i.e. distinguish between)each mobile device. The base system includes two half capacitorarmatures, and each mobile device includes two half capacitor armatures,and one resistor of a predefined value (a characteristic value).

Thus, in certain embodiments based on the system shown in FIG. 3, withthe appropriate choice of values for C, Rb and frequency of the inputsignal, the DC value at the terminal 400 is proportional to theresistance of the particular mobile device 2A or 2B arranged in thefirst position P1. In such arrangements, one would typically work withRC«T. The signal detection means 4 of FIG. 3 enables the system tomeasure the peak value of the signal developed at the second capacitorplate 12. A small variation in capacitor value (i.e. of the totalcapacitance C defined by the first and second capacitors C1, C2) willhave very little impact on the output voltage at terminal 400. Thisenables the system to be robust and remain accurate, even if impuritiesor wear and tear appear at the armature level (e.g. degrade the servicesof any dielectric materials covering the electrodes, thereby slightlyaltering the separation of the electrodes when a moveable device is inthe first position P1.

In alternative embodiments, the signal detection means may be arrangedto measure average values of the output signal or average values of thesignal developed directly at the second base electrode 12, in which casecapacitor variation would be more noticeable. This variation incapacitor value can be deliberately used in certain alternativeembodiments to detect different orientations of a mobile device withrespect to the base, in which case different shaped electrodes should beused, such as those illustrated in FIGS. 11, 12, 13, and 14. With thoseelectrodes, depending on the rotation of the moveable device withrespect to the base, the capacitor electrodes or plates will overlap tovarying degrees. This alters the total capacitance of the seriesarrangement of first and second capacitors, and this in turn ismanifested at the second base electrode 12. Thus, in certain embodimentsthe signal detection means can determine the particular orientation of amobile device with respect to the base, when the mobile device isgenerally in the first position.

Returning to embodiments in which we do not wish variations in C toinfluence the output value, it is necessary to work in the RC«T mode. Insuch embodiments, C may practically be a few pF to a few nF. Theresistance Rb then needs to be low enough to allow the energy transferwithin the pulse signal, and high enough to allow the widest range ofRid values to provide the widest signal dynamic. The rectifier diode 43may be used with a 10 MOhm load 44 and a 10 nF capacitor 45 to convertthe peak value at the second base electrode 12 into a proportional DCvalue. One or more comparators may then be used to identify which of themobile devices 2A, 2B is located in the first position from the signalat terminal 400. Comparators may be implemented at low cost, which inconjunction with the simple electrical elements incorporated in themobile devices (i.e. just capacitor electrodes and a resistor) enablesthe entire system to be implemented at low cost.

Referring now to FIG. 4, this shows an electrode arrangement which maybe used in certain embodiments of the invention. Here, the first andsecond base electrodes 11, 12 are each in the form of rectangularplates, and those rectangular plates are arranged parallel to oneanother. The corresponding electrodes of the mobile device 21, 22 arealso in the form of rectangular plates, arranged parallel to oneanother. In this example, each of the plates 11, 12, 21, 22 hassubstantially the same size and shape as the others, and the gapsbetween the electrodes 11 and 12 and the electrodes 21 and 22 are alsothe same. Thus, when the mobile device is brought into close proximitywith the base the four electrodes are able to align closely with eachother and provide a high degree of capacitive coupling between the baseand mobile entity.

Moving on to FIG. 5, this shows part of a system embodying the inventionin which a square wave input voltage signal of period T is applied tothe input terminal 300 connected to the first base electrode 11. Thecomponents of the mobile device enabling its detection by the base unitare shown in the coupled position, such that the square wave applied toterminal 300 results in generation of a detectable signal at the outputterminal 401 which is connected to the second base electrode 12 and thenon-grounded terminal of a base resistor 42. FIG. 6 shows the typicaloutput wave form at terminal 401 when RC»T.

FIG. 7 shows the typical output wave form at terminal 401 when RC isapproximately equal to T.

FIG. 8 shows the output wave form at terminal 401 for RC«T.

Moving on to FIGS. 9 and 10, these respectively show the mobile entityelectrodes and base electrodes which may be utilised in alternativeembodiments of the invention. Here, the mobile entity comprises acentral, circular first electrode 21. Around that electrode arepositioned a plurality of second moveable entity electrodes 221-226.Each of these second moveable entity electrodes is connected to thecentral electrode 21 by a respective resistor 231-236, and each of theseresistors 231-236 has a resistance different from the others. Thecorresponding arrangement of electrodes in the base comprises asubstantially circular first electrode 11 (which has substantially thesame size and shape as the central electrode 21 of the moveable entity).The second base electrode 12 has the same size and shape as each of thesecond electrodes 221-226 of the mobile entity, and is separated fromthe central electrode 11 in a radial direction in the same manner aseach of the second electrodes 221-226 are separated from the centralelectrode 21. These electrode arrangements are utilised in systems wherethe signal detection means is able to distinguish between a number ofdifferent resistor values connecting the moveable entity electrodes.Thus, the electrode arrangements of FIGS. 9 and 10 can be incorporatedin the system which is adapted to identify and distinguish between sixdifferent rotational positions in which the moveable entity can beplaced next to the base.

Moving on to FIGS. 11 and 12, these show alternative electrodearrangements which may be used in other embodiments of the invention.Here, the first and second base electrodes are each in the form of asectorial plate, and those plates are arranged adjacent one another suchthat together they substantially comprise a semicircular sector. Thefirst and second moveable entity electrodes 21 and 22 have the samesizes and shapes as the base electrodes. It will be appreciated that themobile device can be positioned generally next to the base and thenrotated to vary the amount of overlap between the mobile device platesand the base plates 11 and 12, thereby changing the total capacitance Cof the first and second capacitors connected in series. In certainembodiments the signal protection means is arranged to detect therotational position of the mobile device with respect to the base fromthe effect that this changing capacitance has on the output signal ofthe second capacitor plate 12.

Referring now to FIGS. 13 and 14, these show electrode arrangementsrelated to those shown in FIGS. 11 and 12. Here, the mobile device andbase electrodes are again generally sectorial, but this time arearranged so that they are diagonally opposed within a nominal circularboundary CB. Again, the output signal from the second base electrode 12is dependent on the total capacitance C, which in turn is dependent uponthe rotational position of the mobile device with respect to the base,which determines the amount of overlap between the respective plates.

Moving on to FIGS. 15 and 16, these show alternative electrodearrangements which are used in other embodiments of the invention. Here,the mobile device comprises first and second electrodes 21, 22, whichare each sectorial, but extend round only a small angle with respect toa notional centre. The base comprises a plurality of pairs of electrodesextending fully around a circle (although only a few are shown in thefigure for clarity) each of these base electrodes is sectorial. A firstpair of base electrodes comprises a first electrode 111 and a secondelectrode 121. A second pair of electrodes comprises a first electrode112 and a second base electrode 122, and so on. The signal generatingmeans is arranged to provide a time varying input signal to an inputterminal 300 which is connected to each of the first electrodes 111, 112etc of the plurality of pairs. Each of the second electrodes 121, 122etc of the pairs is connected to a ground rail 41 by a respective baseresistor 421, 422 etc and the signal detection means is adapted tomonitor output signals from each of the second base electrodes. It willbe appreciated that, depending on the particular orientation of themobile device with respect to the base, the mobile device electrodes maybe capacitively coupled with any one of a number of different baseelectrode pairs. From the output signals, the signal detection means isthus able to detect the particular orientation of the mobile device withrespect to the base unit.

Referring now to FIG. 17, this illustrates another system embodying theinvention in which a base 1 is adapted to determine whether a mobiledevice 2 is located in a predefined position with respect to the base,and furthermore can determine the identity of the mobile device. Thesystem comprises a signal generator 3 arranged to provide a time varyingsignal to a first capacitor electrode 11. This signal may be a squarewave, a sinusoidal wave, or a wave having some other form suitable forenabling the signal detection means to determine from the signal of thesecond electrode 12 the presence and identity of the mobile device 2.The system comprises circuitry 46 which performs the function of peakdetection and AC to DC signal conversion on the signal from node 401which is connected to the second base electrode 12. That circuitry 46provides a corresponding signal to circuitry 47 which includes at leastone comparator and/or an analogue to digital converter. In embodimentswhere the circuitry 47 comprises a plurality of comparators, thecircuitry 47 is adapted to provide an output signal at one of aplurality of corresponding output terminals 471, 472-47 n, each of theseoutput terminals corresponding to a particular respective mobile deviceidentity. In other words, if the mobile device 2 positioned so as to becoupled to the base electrodes is a first mobile device, having itscharacteristic first value of Rid, then an output signal is generatedfrom terminal 471. If the device is a second mobile device with adifferent characteristic resistance, then an output signal is generatedat terminal 472 etc. In certain embodiments, the base also comprisescircuitry 48 which is arranged to receive the output signals from theterminals 471-47 n and perform application dependent processing, basedon the detected mobile identity or identities.

Referring now to FIGS. 18-21, these show different arrangements of baseand mobile device electrodes which may be incorporated in embodiments ofthe invention. In FIG. 18, the base 1 comprises a layer of dielectricmaterial 150 which covers the first and second base electrodes 11, 12.The layer 150 thus ensures that no direct electrical contact can be madeto the base electrodes. A variety of materials may be used for thiscovering 150, for example plastic, paper, or other insulating materials,which may be rigid or flexible. The mobile device 2 has its first andsecond electrodes 21 and 22 exposed in this example, each one beinglocated on an external surface 210 of the device. The mobile deviceelectrodes can thus be brought into direct contact with the insulatinglayer or covering 150 on the base to bring them as close as possible tothe corresponding base electrodes, thereby increasing the capacitivecoupling between the base and mobile device.

Referring to FIG. 19, in this alternative arrangement the mobile devicecomprises an insulating layer or covering 250, which covers the mobiledevice electrodes 21, 22. The base electrodes 11, 12 are now exposed,being provided on an external surface 100 of the base 1.

Referring now to FIG. 20, in this arrangement each of the base andmobile device comprises a respective insulating layer, covering, orcoating 150, 250, covering its respective electrodes. Generally, it isdesirable to make these coverings as thin as possible to increase thecapacitive coupling between the base and device 2.

FIG. 21 shows an alternative arrangement in which the base electrodes 11and 12 are embedded in the body of the base, slightly below an externalsurface 100. The moveable device electrodes 21, 22 and connectingresistor 23 are comprised in a tag or label 280 which is attached to theremaining part of the mobile device 2. Thus, an identifying tag or label280 can conveniently be applied to a moveable device to enable detectionand identification of that device relative to a base 1.

Referring now to FIG. 22, this shows another system embodying theinvention. Here the base 1 comprises a plurality of pairs of baseelectrodes 11A, 12A-11D, 12D each associated with a particular positionP1A-P1D at which one of a plurality of mobile devices 2A-2D can belocated with respect to the base. The base 1 comprises signal supplymeans 3 which comprises a signal generator 302, a multiplexer 303, and acontroller 301. The signal generator 302 supplies a time varying signalto the multiplexer and the controller 301 controls the multiplexer 303to apply the time varying signal to a selected one or plurality of thefirst base electrodes 11A/11D. The base 1 also comprises signaldetection means 4 which comprises a controller 401, multiplexing means403, and signal processing means 402. The controller 401 controls themultiplexing means 403 to selectively direct the output signal from anyone of the second base electrodes 12A-12D to the signal processing means402. Thus, the controllers 301 and 401 can operate so that each of thepairs of base electrodes is selectively energised and monitored (whichmay also be described as selectively poling these pairs) to checkwhether one of the mobile devices 2A-2D is positioned over thatrespective pair. Each of the mobile devices 2A-2D comprises a respectivepair of first and second electrodes, and a respective resistor 23A-23Dconnecting those electrodes. The system is thus able to detect thepositioning of any one of the mobile devices at any one of the positionsP1A-D, and furthermore the base can detect which mobile device ispositioned at each location.

Referring now to FIG. 22A, this shows an alternative electrodearrangement used in certain embodiments of the invention. Here, the pairof base electrodes comprises a central first electrode 11, surrounded byan annular second electrode 12. The electrodes 21 and 22 of the mobiledevice have the same general size and shape, that is they comprise acentral circular electrode 21 and an outer annular electrode 22. Whenthe electrodes are arranged correctly next to one another, with thecentral electrodes aligned with one another, the capacitive couplingbetween the two is large, and is unaffected by the particular rotationalorientation of the moveable device electrodes with respect to the base.

Referring now to FIGS. 23-30, these show further embodiments of theinvention. These embodiments can be regarded as disclosing a proximityfield communication technique which can provide contactless single wireenergy and/or data transfer (which may be bidirectional).

Referring in particular to FIG. 23, this illustrates the basic principleof these embodiments, decoupling an AC signal with two half capacitorarmatures 11, 21, that when brought close enough are capacitivelycoupled to form a first capacitor C1. Signal variations applied to thefirst capacitor armature CX1 (11) are transmitted to the second halfcapacitor armature CX2 (21). The system generally comprises a base 1comprising a first base electrode 11 and signal supply means arranged tosupply a first time-varying electrical signal S1 to the first baseelectrode 11. The components of the system in the right half of thefigure are the components of the first moveable entity 2 which comprisesthe first moveable entity electrode 21 and circuitry connected to thefirst moveable entity electrode 21. In this example, the circuitrycomprises a first node N1 connected to the electrode 21, a second nodeN2, and a third node N3. The circuitry also comprises a first diode D1connected in the forward direction between nodes N1 and N2, and a seconddiode D2 connected in the forward direction between nodes N3 and N1.Node N3 is connected to a virtual ground conductor. A capacitor C isconnected between the nodes N2 and N3, where C is much C1. The firsttime varying signal S1 supplied to the first electrode 11 is squarewave, having amplitude V in and frequency F in. By means of the signalS1 and capacitive coupling between the plates 11 and 21, a power outputmay be extracted from the nodes N2 and N3, where that power output is afunction of half C1 V in²×F in.

In other words, when the square wave signal S1 is applied to electrode11, the positive edge is transmitted via the top diode D1, then thenegative edge will create the return with the bottom diode D2. There isno electric return, as there is only one pole, the electric return iscreated locally. Efficiency is improved with the number of electronsavailable at the virtual ground.

Referring now to FIG. 24, this shows another embodiment of theinvention. Here, the base 1 comprises signal supply means 3 adapted toprovide the first time varying signal to the electrode 11, and alsocomprises signal detection or sensing means 4 adapted to detect anelectrical signal from the first base electrode 11. Thus, the sensingmeans 4 can detect when the first moveable entity 2 is in the firstposition, with the capacitor plates 11 and 21 coupled, by means of thesignal sensed on capacitor plate 11. In this example the first moveableentity comprises a resistor R connected between the second and thirdnodes. The time varying signal applied to the first capacitor plate 11results, by means of coupling with the second electrode 21, in a currentbeing driven through the resistor R, which in turn results in a returnsignal being supplied to the second capacitor plate 21, which in turnprovides a signal on the first capacitor plate 11, which is then sensedby the sensing means. Thus, the system can detect when the firstmoveable entity is in the first position. Furthermore, in certainembodiments, the system can detect, via the return signal on the firstcapacitor plate 11 the identity of the moveable entity arranged in thefirst position (different moveable entities may employ different valuesfor the resistor R, and this in turn influences the signal picked up bythe sensing means 4 in response to the initial driving of capacitorplate 11 with the first time-varying signal). Thus, a moveable entity(or mobile device) can be identified through its local load, with onepole as opposed to two poles as described previously in connection withalternative aspects and embodiments.

Moving on to FIG. 25, this shows how multiple voltages can easily begenerated. In this configuration, the system can be used to split energyand data sent and data received, with one pole as an input but multiplehalf capacitors. Thus, in the system of FIG. 25, the base 1 includes apair of first capacitor plates 11 a and 11 b, and the moveable entity 2comprises corresponding capacitor plates 21 a and 21 b which, when theentity is in the aligned position, form capacitors C1 a and C1 b withthe base. The components of the moveable entity circuitry are shown inthe figure, and it will be seen that nodes N3 a and N2 b are connectedto ground in this example (or at least virtual ground). Capacitivecoupling in the illustrated configuration results in two output voltagesbeing developed (between nodes N2 a and N3 a, and N2 b and N3 brespectively), when the time varying signal is supplied to the firstcapacitor plates 11 a and 11 b.

Referring now to FIG. 26, this shows a further embodiment in which thebase 1 comprises energy transmission or energy sending means 31 arrangedto provide the time varying signal in the form of a square wave or signwave to capacitor plate 11. The base also includes data sending or datatransmission means 32 adapted to encode the signal supplied to the firstcapacitor plate 11 with data, such that the first time varying signalcarries data. The base 1 also comprises data receiving or dataextraction or detection means 33 arranged to detect data on a signaldeveloped on capacitor plate 11 by means of coupling with the moveableentity capacitor plate 21. In this embodiment, the moveable entitycomprises a first portion 201 in a form of a plastic bottle filled witha liquid or solid, and a second portion 202 which includes the capacitorplate 21 and connected circuitry. The plastic bottle is arrangedadjacent the first capacitor plate 11 and the second capacitor plate 21is attached to a side surface of the plastic bottle, such thatcapacitive coupling between the plates 11 and 21 is by means of theplastic bottle and its contents. The moveable entity circuitry comprisesmeans for receiving data and decoding data 200 which can also bedescribed as data detection means 200. This data detection means isconnected to the second and third nodes N2, N3 and is adapted to extractdata that was carried by the signal supplied to the first capacitorplate 11. The circuitry further comprises data transmission means 201(which can also be described as data sending means, or a load modulationmeans, or a frequency or amplitude modulator) and this data transmissionmeans 201 is also attached to the second and third nodes. This unit 201is operable to generate a time varying signal on the second capacitorplate 21 which carries data, and that data can then be detected by thedata receiving means 33 of the base by means of the capacitive couplingbetween the plates 11 and 21 via the container and its contents. Thecircuitry also comprises power supply means 202, which can also bedescribed as energy receiving and processing means, and this powersupply 202 is adapted to receive power from the base 1 via thecapacitive coupling between the plates 11 and 21 and power the datareceiving and sending means 200, 201. This power supply means 202 isalso connected to the second and third nodes.

It will be appreciated that the system of FIG. 26 can be operated in anumber of different ways. For example, energy only can be sent fromplate 11 and received at plate 21. Energy and data can be sent fromplate 11 and received at plate 21. Energy and data can be sent fromplate 11 and received at plate 21, as well as data can be sent fromplate 21 and received at plate 11. Multiple wave forms may be used tosend and/or receive energy, for example square waves, sinusoidal waves,triangular waves, etc. Multiple techniques can be used for transmittingand receiving data, in either direction, for example amplitudemodulation, frequency modulation, load modulation, etc.

Referring now to FIG. 27, this shows part of an alternative system wherethe first portion of the moveable entity is a metal can or container,having a metal container wall 2011. Coupling between the capacitor plate11 and 21 is via the container wall 2011, and the system furthercomprises dielectrics arranged between the capacitor plates 11 and themetal wall 2011.

Referring now to FIG. 28, this shows a system similar to that shown inFIG. 27, but incorporating only one dielectric. Indeed, only one of thehalf capacitor armatures needs to have a dielectric position betweenitself and the metal container wall 2011 for the proximity fieldcommunication to work.

Referring now to FIG. 29, this shows another system embodying theinvention. Here the first moveable entity portion is a plastic container(bottle) having a plastic wall 2011 and filled, at least partly, withcontents 2012. The “transmitter” electrode 11 is arranged at the base ofthe container, and the “receiver” electrode 21 is attached to a side ofthe container and has the form of a label. The label includes adielectric layer arranged between the container wall and the electrode21. The label also comprises the circuitry connected to the capacitorplate 21, although the circuitry is not shown in the figure. In thisarrangement, the liquid 2012 inside the container is part of theproximity field communication system, and is needed to operate. Thisprinciple can also be used for level detection.

Referring now to FIG. 30, this shows another system embodying theinvention where the first moveable entity first portion is a metalcontainer (e.g. an aluminium can) and again the second portion of themoveable entity is in the form of a label comprising the electrode 21and associated circuitry (not shown in the figure). Here, the liquidinside the container is not part of the proximity field communicationsystem, so the system will work even if the container is empty. In otherwords, the metal wall of the container 2001 provides sufficiently goodcoupling between the capacitor plate 11 and 12, even without thepresence of any contents inside the container. Thus, the metal containeris part of the proximity field communication system, creating anintermediate capacitor armature between plates 11 and 21.

Throughout the description and claims of this specification, the words“comprise” and “contain” and variations of them mean “including but notlimited to”, and they are not intended to (and do not) exclude othermoieties, additives, components, integers or steps. Throughout thedescription and claims of this specification, the singular encompassesthe plural unless the context otherwise requires. In particular, wherethe indefinite article is used, the specification is to be understood ascontemplating plurality as well as singularity, unless the contextrequires otherwise.

Features, integers, characteristics, compounds, chemical moieties orgroups described in conjunction with a particular aspect, embodiment orexample of the invention are to be understood to be applicable to anyother aspect, embodiment or example described herein unless incompatibletherewith. All of the features disclosed in this specification(including any accompanying claims, abstract and drawings), and/or allof the steps of any method or process so disclosed, may be combined inany combination, except combinations where at least some of suchfeatures and/or steps are mutually exclusive. The invention is notrestricted to the details of any foregoing embodiments. The inventionextends to any novel one, or any novel combination, of the featuresdisclosed in this specification (including any accompanying claims,abstract and drawings), or to any novel one, or any novel combination,of the steps of any method or process so disclosed.

The reader's attention is directed to all papers and documents which arefiled concurrently with or previous to this specification in connectionwith this application and which are open to public inspection with thisspecification, and the contents of all such papers and documents areincorporated herein by reference.

The invention claimed is:
 1. A system comprising a base and at least afirst moveable entity, the first moveable entity being separate andfreely moveable with respect to the base and positionable in at least afirst position with respect to the base, the base comprising at least afirst base electrode, and the first moveable entity comprising at leasta first moveable entity electrode, and the first base electrode and thefirst moveable entity electrode being arranged to couple to form a firstcapacitor when the first moveable entity is in said first position, thebase further comprising signal supply means, arranged to supply a firsttime-varying electrical signal to the first base electrode, and thefirst moveable entity further comprising first circuitry connected tothe first moveable entity electrode, wherein said base is arranged topower said first circuitry via said first time-varying electrical signaland the coupling between the first base electrode and the first moveableentity electrode when the first moveable entity is in the firstposition, and wherein said first circuitry includes a virtual ground. 2.A system in accordance with claim 1, wherein said first circuitry isarranged to create a local electrical return.
 3. A system in accordancewith claim 1, wherein said first circuitry comprises: a first node,connected to the first moveable entity electrode, a second node, and athird node; a first diode connected between the first node and thesecond node to allow current flow from the first node to the second nodeand block current flow from the second node to the first node; and asecond diode connected between the third node and the first node toallow current flow from the third node to the first node and blockcurrent flow from the first node to the third node.
 4. A system inaccordance with claim 1, wherein the base further comprises signaldetection means arranged to detect an electrical signal from the firstbase electrode.
 5. A system in accordance with claim 4, wherein thesignal detection means is adapted to determine whether the firstmoveable entity is in said first position from the electrical signalfrom the first base electrode.
 6. A system in accordance with claim 4,wherein the signal detection means is adapted to determine an identityof the first moveable entity when the first moveable entity is in saidfirst position from the electrical signal from the first base electrode.7. A system in accordance with claim 4, wherein said first circuitry isarranged to provide a second time-varying electrical signal to the firstmoveable entity electrode, the second time-varying electrical signalcarrying data, and the signal detection means is adapted to detect saidsecond time-varying signal when the first moveable entity is in saidfirst position.
 8. A system in accordance with claim 7, wherein thefirst moveable entity includes data transmission means configured togenerate at least part of the second time-varying electrical signal. 9.A system in accordance with claim 3, wherein said first circuitryfurther comprises a second capacitor connected between the second nodeand the third node.
 10. A system in accordance with claim 9, wherein afirst voltage is developed across the second capacitor (i.e. between thesecond and third nodes) in response to the first time-varying electricalsignal being applied to the first base electrode when the first moveableentity is in said first position.
 11. A system in accordance with claim9, wherein said first circuitry further comprises a first resistorconnected between the second node and the third node.
 12. A system inaccordance with claim 11, wherein an electrical current is driventhrough said first resistor in response to the first time-varyingelectrical signal being applied to the first base electrode when thefirst moveable entity is in said first position.
 13. A system inaccordance with claim 9, wherein said first moveable entity furthercomprises data transmission means connected to the second and thirdnodes and adapted to supply a second time-varying electrical signalcarrying second data to the first moveable entity electrode.
 14. Asystem in accordance with claim 13, wherein said first moveable entityfurther comprises power supply circuitry connected to the second andthird nodes, adapted to receive power via the second and third nodeswhen the first moveable entity is in said first position, and adapted topower the data transmission means using said received power.
 15. Asystem in accordance with claim 1, wherein the base comprises only asingle electrode (i.e. the first base electrode), and the first moveableentity comprises only a single electrode (i.e. the first moveable entityelectrode).
 16. A system in accordance with claim 1, wherein the basecomprises a second base electrode coupled to the first base electrodeand the first moveable entity comprises a second moveable entityelectrode, and the second base electrode and second moveable entityelectrode are arranged to couple to form a third capacitor when thefirst moveable entity is in said first position.
 17. A system inaccordance with claim 16, wherein the first moveable entity comprisessecond circuitry connected to the second movable entity electrode, andthe second circuitry is connected to the virtual ground.
 18. A system inaccordance with claim 17, wherein said second circuitry comprises: afourth node, connected to the second moveable entity electrode, a fifthnode, and a sixth node; a third diode connected between the fourth nodeand the firth node to allow current flow from the fourth node to thefifth node and block current flow from the fifth node to the fourthnode; and a fourth diode connected between the sixth node and the fourthnode to allow current flow from the sixth node to the fourth node andblock current flow from the fourth node to the sixth node.
 19. A systemin accordance with claim 18, wherein said second circuitry furthercomprises a fourth capacitor connected between the fifth node and thesixth node.
 20. A system in accordance with claim 19, wherein a secondvoltage is developed across the fourth capacitor (i.e. between the fifthand sixth nodes) in response to the first time-varying electrical signalbeing applied to the second base electrode when the first moveableentity is in said first position.